Separation of naphthalenic from nonnaphthalenic hydrocarbons



United States Patent 3,132,07 8 SEPARATIGN 0F NAPHTHALENIC FROM NON- NAPHTHALENIC HYDROCARBONS Peter Stanley Backlund, Anaheim, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California Filed Mar. 26, 1962, Ser. No. 182,491 20 Claims. (Cl. 20242) This invention relates to the recovery of naphthalenic hydrocarbons from mixtures comprising the same, and in particular concerns a method of treating hydrocarbon mixtures boiling within the 390-520 F. range and containing naphthalene and/ or alkyl-substituted naphthalenes for the purpose of recovering said naphthalenic hydrocarbons in concentrated form.

, The expanding use of naphthalene and alkylnaphthalenes for the production of dicarboxylic acids useful in manufacturingsynthetic resins and fibers has created considerable interest in the recovery of these napthalenic hydrocarbons from hydrocarbon fractions of petroleum origin. vIt is well known that certain fractions obtained from petroleum refining operations, e.g., catalytic cracking and reforming, contain considerable quantities of naphthalene and alkylnaphthalenes. However, such fractions also contain large quantities of other hydrocarbon types which have boiling points very close to those of the aforesaid naphthalenic hydrocarbons or which form azeotropes therewith. In either case, satisfactory separationof the naphthalenic from the non-naphthalenic hydrocarbons cannot be accomplished by fractional distillation.

Accordingly, theprincipal object of the present invention is .the provision of an improved method for treating hydrocarbon mixtures boiling within the 390-520 F. range and comprising naphthalene and/ or .alkylnaphthalenes to separate said naphthalenic materials from nonnaphthalenic hydrocarbons present in the mixture. A more particular object'of the invention is to provide a method whereby non-naphthalenic hydrocarbons boiling in the naphthalene range, that is, within the range of about 400-450 F., can be readily separated from mixtures ofsuch hydrocarbons with naphthalene. Other and relatedobjects will become apparent to those skilled in the art as the description of the invention proceeds.

' I have discovered that the above objects and attendant advantages can be realized in an azeotropic distillation process employing a relatively non-corrosive N-alkylpyrrolidone, of proper boiling point and solubility characteristics for the purpose, as the azeotrope former. The boiling point of the azeotrope former should, for best results, be sufiiciently lower than the boiling range of the feed fraction to permit good recovery of the non-naphtha-- lenic hydrocarbons in the azeotropic overhead fraction. It is, of course, evident that as the boiling point of the azeotrope former approaches the boiling range of the feed fraction, a point is ultimately reached beyond which no practical fractionation of the feed takes place. From the standpoint of boiling point, the azeotrope former of preferred applicability for our purpose is N-methylpyrrolidone which boils at 388 F. As the alkyl group increases in size, the boiling point of the alkyl-substituted pyrrolidone also.increases. This stepwise boiling point increase is of such character as to limit the class of azeotrope formers suitable for our process to those N-alkylpyrrolidones having alkyl groups of four or less carbon atoms.

The selection of suitable azeotrope formers from a boiling point standpoint is consonant with such a selection from the standpoint of solubility characteristics. To be more explicit, as the alkyl group of the N-alkylpyrrolidone increases in size, the solubility of the material in the non-naphthalenic hydrocarbons of the feed increases. Such an increase is undesirable since it mitigates against good phase separation of the condensed azeotropic overhead. Consequently, a line of separation between suitable and unsuitable N-alkylpyrrolidones for use in our invention must be drawn, and, as indicated above, the location of this line based on solubility coincides substantially with its location based entirely upon boiling points.

I have found that the N-alkylpyrrolidones of the abovenoted class form azeotropes of unusually low boiling points with non-napthalenic hydrocarbons boiling Within the 390-520 F. range, so that by admixing such an N- alkylpyrrolidone with a mixture comprising naphthalenic and non-naphthalenic hydrocarbons boiling within said range, and subjecting the resulting mixture to distillation, an exceptionally eflicient separation of the two types of hydrocarbons can be achieved. The non-naphthalenic hydrocarbons distill overhead in the form of low boiling azeotropes with the N-alkylpyrrolidone, leaving the naphthalenic material behind as distillation bottoms. The azeotropic distillate is rich in hydrocarbons and has a relatively low heat of vaporization, so that the amount of heat required to separate a unit volume of non-naphthalenic hydrocarbons from the feed mixture is relatively low.

I have discovered that the N-alkylpyrrolidones (hereinafter the term N-alkylpyrrolidones will, unless otherwise indicated, be employed to denote those having alkyl groups of 4 carbon atoms or less) exhibit a highly selective action toward the non-naphthalenic hydrocarbons when employed as azeotrope formers in the above manner and hence lower reflux ratios and fewer plates in the distillation column are required to effect the desired separations. Moreover, the N-alkylpyrrolidones form two phases with the non-naphthalenic aromatic hydrocarbons taken overhead, so that in many instances substantially complete separation of the azeotrope former from the distillate can be achieved by simple gravity settling, without the necessity of utilizing elaborate secondary equipment for that purpose. Following removal of non-napthalenic hydrocarbons, the naphthalene contained in the remaining bottoms fraction can be easily recovered by non-azeotropic distillation, or by any other desired means.

Considering now the process of my invention in greater detail, the feedstock entering said process may be any mixture of hydrocarbons comprising naphthalene and/ or alkylnaphthalenes and at least one non-naphthalenic hydrocarbon which cannot be separated from the naphthalenic components by simple fractional distillation. The term naphthalenic hydrocarbon is herein employed to designate a hydrocarbon compound whose molecule contains the characteristic naphthalene grouping:

Conversely, the term non-naphthalenic hydrocarbon designates a hydrocarbon compound whose molecule does not contain said grouping. Thus, the non-naphthalenic hydrocarbons which may be present in the feedstock include aliphatic compounds such as dodecane and higher isomeric paraifins and corresponding olefins; naphthenic compounds such as cyclohexylheptene, hexylcyclohexane, dicyclohexyl, and decahydronaphthalene; benzenoid compounds such as triethylbenzene, dimethylindane, ethylindene, etc.; and partially hydrogenated naphthalenic hy drocarbons such as methyltetralin, dimethyltetralin, dihydronaphthalene and methyldihydronaphthalene. The naphthalenic hydrocarbons which may be present in the event, it is generally true that the narrower the 3 feedstock include naphthalene, the methylnaphthalenes, the dimethylnaphthalenes, the ethylnaphthalenes, the isopropylnaphthalenes, etc.

While the hydrocarbon feedstocks to the process of my invention can contain any or all of the above-named compounds, the process is particularly applicable for the treatment of hydrocarbon mixtures containing naphthalene and contaminated mainly with aromatic hydrocarbons such as alkylbenzenes, alkyltetralins, alkylindanes, and thelike, boiling within the naphthalene range and thereabouts, e.g., from about 400 to about 450 F. It is known that naphthalene fractions containing like-boiling parafiin hydrocarbons can be purified by azeotropic distillation with various azeotroping agents. However, a more difficult problem of separation is involved in mixtures such as those just named contaminated mainly with aromatic hydrocarbons. Petroleum fractions of this nature can be derived from various hydrocarbon conversion and refining processes commonly used in the industry, such as for example, catalytic reforming, catalytic cracking, thermal cracking and the like. In particular, catalytic reforming of naphthas produces a heavy reformate fraction boiling above about 400 R, which may contain from about 40 to about 80% lenes.

The feedstocks suitable for treatment as taught herein are not limited to those of conventional petroleum refining origin and may be from any source, such as from destructive distillation or hydrogenation of coal processes or shale oil processes. Usually, however, the feedstock will be of petroleum origin. While the feedstock may be one boiling over the entire 390520 F. range, it 'will usually be one boiling over only a selected portion of such range (e.g., the 4004 50 F. fraction described above or a fraction boiling at 450470 F. and comprising monomethylnaphthalenes, etc.) and may of course contain some components boiling somewhat belows or (less desirably) above said range. The feedstock may also be one which has been pretreated to remove part of the naphthalenic components, e.g., it may be a dealkylated petroleum hydrocarbon reformate fraction from which at least part of the naphthalene has been previously separated by crystallization.

It will be apparent to those skilled in the art that feedstocks boiling over the entire 390 520" F. range which contain both naphthalenic and non-naphthalenic hydrocarbons distributed throughout that range do not, when subjected to our azeotropic distillation treatment, yield a continuous azeotropic overhead. Accordingly, to make a practical naphthalenic-non-naphthalenic separation of such mixtures by distillation means alone, I prefer to first separate the mixture into appropriate fractions by straight distillation and then to distill azeotropically selected fractions, selecting an al-kylpyrrolidone of optimum boiling point for the particular fraction involved.

Best results are achieved in the practice of my invention when the feed to any given azeotropic distillation step has a boiling point range spread no greater than about 50 F. It is of course desirable, in many cases, to have much narrower boiling point spreads, as exemplified by the monomethylnaphthalene fractions boilingfrom about 450 to about 470 F. referred to above. In any boiling point spread of a feed fraction, the cleaner will be the split between its naphthalenic and non-naphthalenic fractions in our azeotropic distillation operation. The boiling point range from about 390 to about 520 F. is sufiiciently broad to encompass the three naphthalenic hydrocarbon fractions, namely, the naphthalene fraction, the monomethylnaphthalene fraction and the dimethylnaphthalene fraction, most often encountered in naphthalene dealkylation feedstocks.

My invention has particular utility for the treatment of hydrocarbon fractions fitting the above-indicated categories which contain naphthalene fractions comprising naphthalene and methylnaphthapetroleum fractions in which the naphthalene fraction boils over the entire range from about 410 to about 450 F. and one or more of the alkylbenzenes, alkyltetralins and alkylindanes comprises the non-naphthalenic hydrocarbon material. More specifically, petroleum fractions within the above class which have been found partieularly amenable to treatment by the method of this invention are those boiling above about 400 F. which include, as non-naphthalenic hydrocarbons, alkylbenzenes, alkyltetralins and al klindanes boiling over the range from about 410 to about 435 F.; heavy naphtha reforr'nates boiling above about 400 F. and including a naphthalene fraction boiling over the range from about 410 to about 450 F. which preferably contains alkylbenzenes, alkyltetralins and alkylindanes; and heavy naphtha reformates which have been subjected to catalytic hydrodealkylation, boiling above about 400 F. and including a naphthalene fraction boiling over the range from about 410 to about 450 R, which naphthalene fraction preferably contains alkylbenzenes, alkyltetralins and alkylindanes.

Procedure-wise, my process is carried outas a conventional azeotropic distillation'operation, and any of the techniques commonly applied to such types of operation are applicable to the present process. In its simplest embodiment, namely, batch distillation, the process consists essentially of adding to the feedstock sufiicient N-alkylpyrrol-idone to form :azeotropes with the non-naphthalenic components, and thereafter distilling the mixture in a reasonably efficient distillation column. The azeotropic distillate is condensed and passed to a separator where the condensate is allowed to separate by gravity into two phases, one of which comprises the non-naphthalenic components of the feedstock containing a small quantity of N alkylpyrrolidone and the other of which comprises N-alkylpyrrolidone containing a relatively small quantity of dissolved non-naphthalenic hydrocarbons. Either or both of said phases may be redistilled or otherwise treated to recover the azeotrope former for reuse. The naphthalenic components of the feedstock are contained in the bottoms fraction which constitutes the desired end product of the process.

In practicing the process of my invention on those naphthalene-mon0aromatic hydrocarbon feedstock mixtures for which it is most suitable, I have found that substantially all of the alkylbenzenes, alkyltetralins, and alkylindanes which boil within about 30 F. of naphthalene can be efficiently azeotroped overhead before any substantial amounts of naphthalene appear in the overhead product. Moreover, it is found that the azeotropic overhead is unexpectedly rich in hydrocarbons, containing only about 50 to about 60 percent by weight of N- alkylpyrrolidone, thus minimizing the distillation load and the amount of azeotrope former required.

Attention is now directed to the accompanying drawing, which. illustrates schematically one method of practicing the azeotropic distillation process of this invention on a hydracarbon feedstock comprising naphthalene and close-boiling non-naphthalenic hydrocarbons. The initial feedstock is brought in through line 2 and admitted to distillation column 4 wherein the primary azeotropic distillation takes place. Column ,4 may be a conventional fractional distillation column containing, for example, 20- plates and may be operated at overhead reflux ratios of, e.g., 1:1 to 20:1. ,Azeotroping is continued until substantially all of the non-naphthalenic hydrocarbons boiling within about 10 F, and preferably 20 F., of naphthalene are distilled overhead. The overhead temperatures during the azeotropic distillation will usually range between about 386 and about 390 F., the N-alkylpyrrolidones themselves boiling within the range from about 388 to about 392 F. The azeotropic overhead is taken off through line 6 and is condensed in condenser 8, and the resulting condensate is transferred by line to a liquid phase separator 12. To provide the desired reflux ratio, a portion of the condensate in line 10 may be diverted through line 16 and admitted to the top of column 4.

In phase separator 12, the condensate may separate spontaneously into two phases, or a small proportion of a miscibility reducing agent may be required, depending upon the nature of the feed. If the feed is rich in lower alkylated aromatics a miscibility reducing agent is ordinarily required, but if it is rich in higher alkylated aromatics and/or in naphthenes, adequate phase separation occurs spontaneously. Suitable miscibility reducing agents include anti-solvents for the 'N-alkylpyrrolidones, e.g., paraffinic or naphthenic hydrocarbons such as pentane, decane, cyclohexane or the like. Other suitable miscibility reducing agents are anti-solvents for the nonnaphthalenic hydrocarbons such as water or the like. Preferably, the miscibility reducing agent should be easily separable, as by distillation, from the phase in which it is dissolved. The N-alkylpyrrolidone-rich phase which stratifies in separator 12 will ordinarily contain about 5 to about percent by ,weight of dissolved hydrocarbons, and this solution is continuously recycled via line 14 back to a mid-point in distillation column 4. Makeup N-alkylpyrrolidone can be added to the system via line 13 and valve 15 if necessary or desirable.

' The hydrocarbon-rich phase in separator 12 ordinarily will contain about 5 to about 25 percent by Weight of dissolved N-alkylpyrrolidone. This hydrocarbon-rich phase is'then' transferred via line 18 to fractionating column 20, from which the N-alkylpyrrolidone is distilled overhead via line 22 as an azeotropic distillate with a portion of the non-naphthalenic hydrocarbons and condensed into separator 12. Valves 21 and 23 are normally open and valves 42 and 58 are normally closed when operating column 20.

The azeotropic distillate from column 20, as well as that from column 4, is a minimum boiling azeotrope in the sense that the various azeotropic combinations involved are minimum boiling azeotropes. The non-naphthalenic hydrocarbons are withdrawn as bottoms from column via line 24. a

A naphthalene-containing bottoms fraction is continuously withdrawn from distillation column 4 .via line 26, and transferred to naphthalene fractionating column 28. Since substantially all of the close-boiling non-naphthalenic hydrocarbons have been removed in column 4, the principal separation which is achieved in column 28 is normally the separation of naphthalene from alkylnaphthalenes, such as, for example, methylnaphthalenes. The

naphthalene overhead is withdrawn via line 30 and condensed in cooler 32 to substantially pure naphthalene crys tals melting at about 80? C. These crystals are normally in excess of 99 percent pure. The alkylnaphthalene bottoms fraction from column 28 is withdrawn via line 34 and may be sent to dealkylation facilities, not shown, to produce additional naphthalene. Such dealkylation facilities may be those of any conventional catalytic hydrodealkylation process. An especially preferred technique for I dealkylating methylnaphthalenes employs steam and hydrogen at elevated temperatures and pressures over a cobalt-molybdatecatalyst as is more particularly described in U.S. Patent No. 2,734,929 to Doumani. Where the column 28 bottoms product is subjected to dealkylation, the resulting dealkylate can be recycled to admixture with the feed to column 4 if desired.

The foregoing is not to be considered limitative of the scope of my process. As those skilled in the art will appreciate, other conventional azeotropic techniques may be employed, and other conventional methods such as fractional crystallization, solvent extraction or azeotropic distillation may be employed to recover naphthalene from theazeotroping bottoms. In addition, conventional techniques for carrying out the various other phases of my process may be employed in place of, or in addition to, those techniques specifically described. For example, it is within the scope of the invention to substitute a solvent recovery step for the column 20 distillation to recover the azeotrope former from the non-naphthalenic hydrocarbon phase from phase separator 12. One such method is to recover N-alkylpyrrolidone from the hydrocarbon rich phase by extraction with water, or other suitable solvent, whereby a non-naphthalenic hydrocarbon material essentially free of N-alkylpyrrolidone is obtained. In this embodiment, the hydrocarbon rich phase from separator 12 is fed from line 18 to extraction column 44 through line 40. Valves 21 and 23 are closed and valve 42 is opened. The water or other extraction solvent enters column 44 through line 45 and the non-naphthalenicv hydrocarbons exit through line 48. The N-alkylpyrrolidone-water mixture is withdrawn from extraction column 44 and transferred to solvent recovery column 52 through line 51}. Solvent recovery column 52 is a conventional distillation column operated to distill, the water or other solvent overhead through line 54 to recover theN-alkyh pyrrolidone as a bottom product. The N-alkylpyrrolidone is withdrawn from solvent recovery column 52 and returned to the process Via line 56. Valve 58 must be opened to permit flow of the N-alkylpyrrolidone to distillation column 4. Water is the preferred solvent for such an operation because of its high selectivity for the N- alkylpyrrolidone in the presence of hydrocarbons and its relatively low boiling point. The latter property is, of course, important in that it permits ready separation of the water from the resulting extract phase by simple distillation means. In this connection, it is noted that its relatively low boiling point makes it a simple matter to remove extraneous water from any liquid stream or product in our process by distillation means. One possible. source of such extraneous Water is its useas a miscibility reducing agent in accordance with prior suggestion herein. Water does, not form an azeotrope, at least to any significant extent, with any of the materials involved in the practice of my invention.

' The effectiveness of my process is more particularly illustrated by the following examples. are, however, not to be construed as limitative, but merely exemplary.

EXAMPLE I This example is included to illustrate the inefiicacy of straight'distillation as a means of separating naphthalenic from'non-naphthalenic hydrocarbons in admix-- ture therewith.

The 400550+ P. fraction of a reformate product was separated therefrom by distillation and subjected to a hydrocarbon type analysis. The results of the analysis are set forth below.

The distribution of the naphthalenes was found to be as follows '(the figures representing Weight percentages of the total sample) Percent b Components: weight y regs 8. 11 10 21.0 Cull-r2 6.4 CISHM. 1.3 (1141110 0.3 CrsHis 0.1

. The 400-550+ F. reformate fraction was subjected to batch distillation in a 30-plate Oldershaw column at a 10:1 reflux ratio and in the absence of an azeotroping agent. The fractions obtained from the batch distillation These examples were analyzed for hydrocarbon types. Results of these analyses appear in Table 1 below:

small quantities are sufiicient for the purpose. Thus, in the presentexample the ratio of N-methylpyrrolidone to Table 1 Boiling Point,F 400-420 420430 430435 435-440 440-145 445-450 450-455 455-550 450-455 455-470 470-540 540-550 In evaluating the Table 1 data, it will be noted that the bulk of all components of the feedstock except the" higher boiling alkylnaphthalenes distilled off in the fractions within the boiling point range from 400 to 500 F. It will be further noted that none of the six fractions within that range show any practically significant enrichment in either naphthalene or non-naphthalenic hydrocarbons over the starting material.

Turning next to the higher boiling fractions, particularly those between 450 and 540 B, it will be observed that no practical selectivity was effected there either. Thus, while the bulk of the alkylnaphthalene portion of the feed distilled within that range there was also much alkylenbenzene and tetralinindane distillation therein to mitigateagainst economically acceptable selectivity. This was particularly true of the boiling point range from 450 to 465 F.

EXAMPLE II A reformate fraction boiling between 400 and 445 In carrying out the continuous distillation operationof this example, the reformate feedstock is continuously introduced into the distillation column along with the N-methylpyrrolidone. The column is operated to produce 55' overhead vapor stream at a temperature of 386 F. and a bottoms fraction boiling above about 420 F. The latter fraction is continuously withdrawn from the bottom of the Oldershaw column as the process product, and comprises about'90 percent by weight naphthalene.

The overhead from the colunm is condensed and separated into two phases-a hydrocarbon phase comprising primarily non-naphthalenic components of the feedstock, but including about percent by weight N-methylpyrrolidone, and an N-methylpyrrolidone phase. 5

The bottoms product from the azeotropic distillation is subjected to straight batch distillation in a 30-plate Oldershaw column at a reflux ratio of 10:1. The overhead product is a phthalic grade naphthalene of 79 C. melting point. The overall recovery of naphthalene is about 80 percent. 7

The results of this example clearly illustrate the excellent selectivity attainable through the use of N-rnethylpyrrolidone as an azeotrope former in the method of my invention. They also illustrate that such selectivity is not dependent upon the use of large quantities of N- methylpyrrolidone but, on the contrary, that relatively non-naphthalene feedstock hydrocarbons, upon a volume basis, is only 1.2 to 1.

EXAMPLE III This example is illustrative of the separation of nonnaphthalene hydrocarbons from alkylnaphthalenes according to the method of this invention.

A bottoms fraction of a platinum-catalyzed reformate product having a boiling range of 385440 F. is hydrodeal-kylated over a cobalt oxide-molybdenum oxide catalyst to produce a dealkylated product boiling over the range 141 -550 F. This product is fractionally distilled to obtain a light gasoline fraction boiling at 141- 401 F., a naphthalene fraction boiling at 401-438 F a methylnaphthalene t'raction boiling at 456-467 F., and a heavy fraction boiling at 493-550 F. Analysis shows the methylnaphthalene fraction to contain about 90.5 percent by weight of 1- and Z-methylnaphthalenes and about 9.5 percent by weight of non-naphthalenic hydrocarbons, presumably alkyltetralins and alkylindanes. This material, together with 20 percent by weight of N-methylpyrrolidone, is introduced into a 30 plate Oldershaw column and a distillation is carried out therein to yield a bottoms product enriched in methylnaphthalenes.

EXAMPLE IV This example illustrates an azeotropic distillation according to this invention in which N-isobutylpyrrolidone is used as the azeotrope former.

A quantity of a reformate fraction containing 43 weight percent naphthalene and 1 weight percent methylnaphthalene, the remainder being alkanes, naphthenes, alkylbenzenes, tetralins and indanes, together with percent by weight N-isobutylpyrrolidone is introduced into a 30 plate Oldershaw column and a distillation is carried out therein to yield a bottoms product enriched in naphthalene.

It will be apparent that the method of my invention is applicable for use in the separation of many hydrocarbon mixtures other than those described in the above examples. Thus, any hydrocarbon mixture within the reach of this invention can be separated into non-naphthalenic and naphthalenic fractions by azeotropically distilling it in the presence of an N-alkylpyrrolidone in accordance with the teachings herein.

I claim:

1. A process for treating a hydrocarbon mixture boiling witlnn the range from about 390 F. to about 520 F., and comprising naphthalenic and non-naphthalenic components which are not separable by simple fractional distillation, which comprises azeotropically distilling said mixture together with an N-alkylpyrrolidone, in which the alkyl radical contains no more than 4 carbon atoms, to vaporize said non-naphthalenic components together with said N-alkylpyrrolidone as a minimum boiling azeotropic distillate, thereby leaving a bottoms product in which the ratio of naphthalenic to non-naphthalenic hydrocarbons is substantially greater than the ratio thereof in said hydrocarbon mixture.

- 2. The process of claim 1 wherein the hydrocarbon mixture boiling within the range from about 390 F. to about 520 F. has a boiling range spread no greater than about 50 Fahrenheit degrees.

3. 'A process as defined by claim 1 wherein the napthalenic components of said hydrocarbon mixture include naphthalene.

4. The process of claim I wherein the N-alkylpyrrolidone is N-methylpyrrolidone.

5. A process as defined by claim 1 wherein the naph thalenic components of said hydrocarbon mixture comprise methylnaphthalenes.

6. A process as defined by claim 1 wherein the nonnaphthalenic components of said hydrocarbon mixture include at least 1 hydrocarbon type from the class consisting of alkylbenzenes, alkyltetralins and alkylindanes.

7. A process as defined by claim 1 wherein said hydrocarbon mixture is one obtained by fractionally distilling a product obtained by the catalytic dealkylation of a platinum catalyzed refonmate fraction boiling between about 385 F. and about 440 F.

8. A process for treating a hydrocarbon mixture boiling within the range from about 390 F. to about 520 F., and comprising naphthalenic and non-naphthalenic hydrocarbons which are not readily separable by simple fractional distillation means, comprising:

(1) distilling said hydrocarbon mixture together with sufficient added N-methylpyrrolidone to vaporize substantially all of said non-naphthalenic hydrocarbons together with substantially all of said N-methylpyrrolidone as a first minimum boiling azeotropic distillate;

(2) condensing said distillate and allowing the azeotropic condensate to separate into two liquid phases, one phase comprising N-methylpyrrolidone and a minor proportion of non-naphthalenic hydrocarbons and the other phase comprising non-naphthalenic hydrocarbons and a minor proportion of N-methylpyrrolidone;

(3) returning said phase comprising N-methylpyrrolidone and a minor proportion of non-naphthalenic hydrocarbons to step (1);

(4) fractionally distilling said phase comprising nonnaphthalenic hydrocarbons and the minor proportion of N-methylpyrrolidone to obtain a second overhead azeotropic distillate of N-methylpyrrolidone and non-naphthalenic hydrocarbons and a bottoms product comprising non-naphthalenic hydrocarbons;

(5) combining said second overhead azeotropic distillate from step (4) with said first azeotropic distillate from step (1) prior to the condensation and phase separation of step (2); and

(6) recovering from said step (1) distillation, as a bottoms product, a naphthalenic components-rich fraction of said hydrocarbon mixture.

9. A process as defined by claim 8 wherein the naph thalenic fraction of said hydrocarbon mixture includes naphthalene and methylnaphthalenes.

10. A process as defined by claim 8 wherein the non naphthalenic fraction of said hydrocarbon mixture includes at least one hydrocarbon type from the class consisting of alkylbenzenes, alkyltetralins and alkylindanes.

11. A method for the recovery of substantially pure naphthalene from a petroleum fraction comprising naphthalenic and non-naphthalenic components not readily separable by simple fractional distillation, boiling within the range from about 400 F. to about 520 F., which comprises:

(1) subjecting said fraction to azeotropic distillation in admixture with N-methylpyrrolidone until a major proportion of the non-naphthalenic hydrocarbons in said fraction which boil within about 10 Fahrenheit degrees of naphthalene is distilled overhead with N- methylpyrrolidone as an azeotropic distillate; and

10 (2) recovering substantially pure naphthalene from the remaining bottoms fraction.

12. The method of claim 11 in which said non-naphthalenic hydrocarbon components comprise at least one hydrocarbon type from the class consisting of alkylbenzenes, alkyltetralins and alkylindanes.

13. The method of claim 11 in which said non-naphthalenic hydrocarbon components include alkylbenzenes, alkyltetralins and alkylindanes boiling within the range from about 410 F. to about 435 F. 1

14. The method of claim 11 in which said petroleum fraction is a heavy naphtha reformate including a naphthalene fraction boiling over the range from about 410 F. to about 450 F.

15. The method of claim 11 in which said petroleum fraction is a heavy naphtha reformate which has been subjected to catalytic hydrodealkylation, and which includes a naphthalene fraction boiling within the range from about 410 F. to about 450 F.

16. A method for the recovery of substantially pure naphthalene from a petroleum distillate comprising a naphthalene fraction boiling within the range from about 410 F. to about 450 F., said naphthalene fraction also containing alkylbenzenes, alkyltetralins and alkylindanes, which comprises:

(1) subjecting said fraction to azeotropic distillation in admixture with N-rnethylpyrrolidone until substantially all of the non-naphthalenic hydrocarbons in said fraction which boil within about 20 Fahrenheit degrees of naphthalene are distilled overhead as an azeotropic distillate with said N-methylpyrrolidone; V

and

(2) distilling the remaining bottoms fraction in the absence of N-methylpyrrolidone to recover substantially pure naphthalene as an overhead product.

17. The method of claim 16 in which said petroleum distillate is a heavy naphtha reformate boiling within the range from about 400 F. to about 520 F.

18. The method of claim 16 in which said petroleum distillate is a heavy naphtha reformate which has been subjected to catalytic hydrodealkylation.

19. A process for treating a hydrocarbon mixture boiling within the range from about 390 F. to about 520 F., having a boiling range spread no greater than about 50 Fahrenheit degrees, and comprising naphthalenic and nonnaphthalenic hydrocarbons which are not readily separable by simple fractional distillation means, comprising:

(1) subjecting a mixture of said hydrocarbon mixture and N-methylpyrrolidone to a first distillation under conditions such as to separate a first azeotropic distillate consisting essentially of non-naphthalenic hydrocarbons together with N-methylpyrrolidone, from a liquid fraction enriched in naphthalenic hydrocarbons;

(2) condensing said first distillate and allowing it to separate into two liquid phases, a first phase comprising N-methylpyrrolidone and a minor proportion of non-naphthalenic hydrocarbons and a second phase comprising non-naphthalenic hydrocarbons and a minor proportion of N-methylpyrrolidone;

(3) returning said first phase to said first distillation;

(4) subjecting said second phase to a second distillation to obtain a second azeotropic distillate of N- methylpyrrolidone and non-naphthalenic hydrocarbons and a bottoms product comprising non-naphthalenic hydrocarbons; and

(5) combining said second azeotropic distillate with said first azeotropic distilling prior to said condensation and phase separation of step (2).

20. A process for treating a hydrocarbon mixture boiling Within the range from about 390 to about 520 F., and comprising naphthalenic and non-naphthalenic hydrocarbons which are not readily separable by simple fractional distillation means, comprising:

(1) subjecting a mixture of said hydrocarbon mixture (4) subjecting said second phase to a Water extraction treatment to obtain an extract of said N-alkylpyrrolidone and water and a ratfinate comprising non-naphthalenic hydrocarbons; and

(5) recovering the N-alkylpyrrolidone from said extract by distillation of the water therefrom.

References Cited in the file of this patent UNITED STATES PATENTS Nelson Mar. 6, 1956 Weedman Nov. 20, 1956 McKinnis July 10, 1962 

1. A PROCESS FOR TREATING A HYDROCARBON MIXTURE BOILING WITHIN THE RANGE FROM ABOUT 390*F. TO ABOUT 520*F., AND COMPRISING NAPHTHALENIC AND NON-NAPHTHALENIC COMPONENTS WHICH ARE NOT SEPARABLE BY SIMPLE FRACTIONAL DISTILLATION, WHICH COMPRISES AZEOTROPICALLY DISTILLING SAID MIXTURE TOGETHER WITH AN N-ALKYLPYRROLIDONE, IN WHICH THE ALKYL RADICAL CONTAINS NO MORE THAN 4 CARBON ATOMS, TO VAPORIZE SAID NON-NAPHTHALENIC COMPONENTS TOGETHER WITH SAID N-ALKYLPYRROLIDONE AS A MINIMUM BOILING AZEOTROPIC DISTILLATE, THEREBY LEAVING A BOTTOMS PRODUCT IN WHICH THE RATIO OF NAPHTHALENIC TO NON-NAPHTHALENIC HYDROCARBONS IS SUBSTANTIALLY GREATER THAN THE RATIO THEREOF IN SAID HYDROCARBON MIXTURE.
 11. A METHOD FOR THE RECOVERY OF SUBSTANTIALLY PURE NAPHTHALENE FROM A PETROLEUM FRACTION COMPRISING NAPHTHALENIC AND NON-NAPHTHALENIC COMPONENTS NOT READILY SEPARABLE BY SIMPLE FRACTIONAL DISTILLATION, BOILING WITHIN THE RANGE FROM ABOUT 400*F. TO ABOUT 520*F., WHICH COMPRISES: (1) SUBJECTING SAID FRACTION TO AZEOTROPIC DISTILLATION IN ADMIXTURE WITH N-METHYLPYRROLIDONE UNTIL A MAJOR PROPORTION OF THE NON-NAPHTHALENIC HYDROCARBONS IN SAID FRACTION WHICH BOIL WITHIN ABOUT 10 FAHRENHEIT DEGREES OF NAPHTHALENE IS DISTILLED OVERHEAD WITH NMETHYLPYRROLIDONE AS AN AZEOTROPIC DISTILLATE; AND (2) RECOVERING SUBSTANTIALLY PURE NAPHTHALENE FROM THE REMAINING BOTTOMS FRACTION. 